I've been asked about coax connector loss.
One guy even told me that there's 1 dB of
loss each time you insert a connector in line on HF!!!
Nothing could be further from the truth!
Here's a link that put that bogus remark to rest!
Coax loss is another matter!
That same guy also said, "RG-213 doesn't work on two meters, you might just as well use two tin cans and a string"!
A truly stupid statement!
Granted it has more loss at higher frequencies but ALL coax exhibits more loss at higher frequencies!
Picking the type of coax for the frequency of operation also depends on what your intent is.
If you're going to work moon bounce, yes the highest quality lowest loss is desirable but if all you want to do is work local repeaters,
then 213 is just fine! I know, I'm doing it and it DOES work!
A great deal has been written about coax loss and is well worth learning. Google is your friend!